Bottom Line:
How the neurons are recruited as associative memory cells to encode multiple input signals for their associated storage and distinguishable retrieval remains unclear.After associative learning, the neurons and astrocytes in the sensory cortices are able to store the newly learnt signal (cross-modal memory) besides the innate signal (native-modal memory).Such associative memory cells distinguish the differences of these signals by programming different codes and signify the historical associations of these signals by similar codes in information retrievals.

ABSTRACTAssociative learning and memory are essential to logical thinking and cognition. How the neurons are recruited as associative memory cells to encode multiple input signals for their associated storage and distinguishable retrieval remains unclear. We studied this issue in the barrel cortex by in vivo two-photon calcium imaging, electrophysiology, and neural tracing in our mouse model that the simultaneous whisker and olfaction stimulations led to odorant-induced whisker motion. After this cross-modal reflex arose, the barrel and piriform cortices connected. More than 40% of barrel cortical neurons became to encode odor signal alongside whisker signal. Some of these neurons expressed distinct activity patterns in response to acquired odor signal and innate whisker signal, and others encoded similar pattern in response to these signals. In the meantime, certain barrel cortical astrocytes encoded odorant and whisker signals. After associative learning, the neurons and astrocytes in the sensory cortices are able to store the newly learnt signal (cross-modal memory) besides the innate signal (native-modal memory). Such associative memory cells distinguish the differences of these signals by programming different codes and signify the historical associations of these signals by similar codes in information retrievals.

Figure 10: Individual neurons in the barrel cortex can recognize OS and WS from CR-formation mice by encoding their activity patterns. Neuronal activities were recorded by intracellular recording. (A,B) Show that a neuron responds to OS (horizontal bar in A) and WS (horizontal bar in B) with different synaptic integrated events. Blue dash-line illustrates resting membrane potential (−65 mV) for this neuron. (C,D) Illustrate that a neuron responds to OS (horizontal bar in C) and WS (horizontal bar in D) with different spike patterns. Blue dash-line shows resting membrane potential (−65 mV) for this neuron, and red dash-line shows a zero membrane potential for indicating the overshot of action potentials. Calibration bars are 20 mV/2 s. (E) Shows the averaged inter-event intervals from neurons in response to OS and WS (n = 6, p < 0.001; One-Way ANOVA). (F) Shows inter-event intervals from each of six neurons that respond to OS and WS. ***p < 0.001.

Mentions:
In order to confirm that individual neurons were able to recognize associative signals, we further recorded barrel cortical CR neurons intracellularly and analyzed the patterns of their responses to OS and WS. Figures 10A,B shows an example of recording synaptic integrated potentials in response to OS and WS. Figures 10C,D shows an experiment of recording spike bursts in response to OS and WS. Statistical analyses in inter-event intervals (Figures 10E,F) show that the activity patterns in CR neurons are distinct in response to WS and OS (p < 0.001, n = 6; One-Way ANOVA). The result is consistent with that from two-photon cell imaging. The individual neurons in the barrel cortex memorize associative whisker and odor signals, as well as recognize their differences by encoding different responsive patterns in signal retrieval.

Figure 10: Individual neurons in the barrel cortex can recognize OS and WS from CR-formation mice by encoding their activity patterns. Neuronal activities were recorded by intracellular recording. (A,B) Show that a neuron responds to OS (horizontal bar in A) and WS (horizontal bar in B) with different synaptic integrated events. Blue dash-line illustrates resting membrane potential (−65 mV) for this neuron. (C,D) Illustrate that a neuron responds to OS (horizontal bar in C) and WS (horizontal bar in D) with different spike patterns. Blue dash-line shows resting membrane potential (−65 mV) for this neuron, and red dash-line shows a zero membrane potential for indicating the overshot of action potentials. Calibration bars are 20 mV/2 s. (E) Shows the averaged inter-event intervals from neurons in response to OS and WS (n = 6, p < 0.001; One-Way ANOVA). (F) Shows inter-event intervals from each of six neurons that respond to OS and WS. ***p < 0.001.

Mentions:
In order to confirm that individual neurons were able to recognize associative signals, we further recorded barrel cortical CR neurons intracellularly and analyzed the patterns of their responses to OS and WS. Figures 10A,B shows an example of recording synaptic integrated potentials in response to OS and WS. Figures 10C,D shows an experiment of recording spike bursts in response to OS and WS. Statistical analyses in inter-event intervals (Figures 10E,F) show that the activity patterns in CR neurons are distinct in response to WS and OS (p < 0.001, n = 6; One-Way ANOVA). The result is consistent with that from two-photon cell imaging. The individual neurons in the barrel cortex memorize associative whisker and odor signals, as well as recognize their differences by encoding different responsive patterns in signal retrieval.

Bottom Line:
How the neurons are recruited as associative memory cells to encode multiple input signals for their associated storage and distinguishable retrieval remains unclear.After associative learning, the neurons and astrocytes in the sensory cortices are able to store the newly learnt signal (cross-modal memory) besides the innate signal (native-modal memory).Such associative memory cells distinguish the differences of these signals by programming different codes and signify the historical associations of these signals by similar codes in information retrievals.

ABSTRACTAssociative learning and memory are essential to logical thinking and cognition. How the neurons are recruited as associative memory cells to encode multiple input signals for their associated storage and distinguishable retrieval remains unclear. We studied this issue in the barrel cortex by in vivo two-photon calcium imaging, electrophysiology, and neural tracing in our mouse model that the simultaneous whisker and olfaction stimulations led to odorant-induced whisker motion. After this cross-modal reflex arose, the barrel and piriform cortices connected. More than 40% of barrel cortical neurons became to encode odor signal alongside whisker signal. Some of these neurons expressed distinct activity patterns in response to acquired odor signal and innate whisker signal, and others encoded similar pattern in response to these signals. In the meantime, certain barrel cortical astrocytes encoded odorant and whisker signals. After associative learning, the neurons and astrocytes in the sensory cortices are able to store the newly learnt signal (cross-modal memory) besides the innate signal (native-modal memory). Such associative memory cells distinguish the differences of these signals by programming different codes and signify the historical associations of these signals by similar codes in information retrievals.